1. Field of the Invention
The present invention relates to a perforation and image exposure system in which a hole is punched in a plate and an image is exposed.
2. Description of the Related Art
Hitherto, as an image exposure apparatus for creating a printing plate in which an image is exposed on a plate such as an aluminum foil sheet, there is known one in which the plate is wound around a rotating drum, and the plate is irradiated with a light beam according to image data, while the plate is rotated together with the rotating drum, so that the plate is exposed on a scanning basis (cf. for example, Japanese Patent Application Laid Open Gazette TokuKai. 2001-356489 (Page 1, FIG. 2).
By the way, there is known a method in which a punched hole, as a criterion when a plate (the printing plate) after image exposure is wound around a rotary press to perform printing, is formed on the plate before or after the image exposure. There is also known one in which a punch unit for formed such a punched hole is prepared independently of an image exposure apparatus, and the image exposure apparatus is provided with only an exposure function. In case of the use of such a type of structure, there is a need that the image exposure apparatus is used to perform image exposure onto the plate, and the punch unit separated from the image exposure apparatus is used to form a punched hole (the procedure for the image exposure and the punched hole formation is optional).
As mentioned above, in case of the use of an apparatus of an arrangement in which the punch unit is independently separated from the image exposure apparatus, an image exposure process and a punch process are carried out independently of one another. This makes it easy to bring about discrepancy between the exposure position of the plate and the punch position. Discrepancy between the exposure position of the plate and the punch position causes discrepancy between the image exposure position and the printing position using a printing plate. Accordingly, there is a need to implement an exact coincidence between the exposure position of the plate and the punch position.
According to the conventional apparatus as mentioned above, as a method of plate positioning, there is adopted a method of performing positioning in such a way that a puncher is used to form a notch for positioning at the top of the plate, and the notch is engaged with a positioning pin projecting into the rotating drum or a positioning pin provided on the punch unit.
Further, as another method of plate positioning different from the above, there is known a technology of performing plate positioning in such a way that a mark referred to as a “register mark” is applied by an exposure to a place out of the image area of the plate, and the mark is measured to move the plate in accordance with the mark.
The method of forming a notch by a puncher according to the prior art needs an expensive puncher for forming the notch, and in addition needs frequent exchange of blades to form notches on a large number of plates. Accordingly, these aspects involve the cost up.
Further, the method of applying the mark to the plate needs a measurement apparatus for measuring marks for the image exposure apparatus and the punch unit. This aspect also involves the cost up, and in addition involves such a problem that the processing procedure is restricted, since the marks are formed by exposure, and as a result, the exposure step is first and the punch step is later.